1. Field of the Invention
The present invention generally relates to the field of electrical circuits. More particularly, the present invention relates to DC/DC conversion circuits.
2. Background Art
In voltage conversion circuitry, a buck converter is commonly used to convert a high DC voltage to a low DC voltage. A buck converter typically includes a switch between an input and an output of the buck converter (also referred to as a “control switch”) and a switch between the output of the buck converter and ground (also referred to as a “synchronous switch”). The buck converter can also include control circuitry to control the duty cycles of these switches so as to convert a high input voltage to a low output voltage. When the control circuitry is not powered and is not operational to control the switches, conducting current through the switches can damage electrical components by introducing short circuits.
Conventional buck converters utilize enhancement-mode transistors as switches, which are normally off during start up and in the absence of a defined gate voltage, to avoid conducting current through the switches while the control circuitry is not fully powered up. The switches typically comprise silicon transistors, which can be easily formed as enhancement-mode transistors. However, III-nitride transistors offer advantages over silicon transistors when utilized in buck converters due to, for example, the higher voltage handling capability of III-nitride transistors. III-nitride transistors are less costly and more efficient to mass-produce as depletion-mode transistors, which are normally on during start up and in the absence of a defined gate voltage, and which can unfortunately introduce short circuit while control circuitry is not fully powered up.
Thus, there is a need in the art for voltage conversion circuitry that can utilize cost efficient depletion-mode III-nitride transistors, while avoiding damage caused by potential short circuits when control circuitry is not fully powered up.